Please refer to FIG. 1(a) showing the conventional master-slave circuit for parallel power supplies. The master-slave current distribution circuit 1 includes the voltage amplifier 11, the impedance 12, the power converting unit 13, the current detecting unit 14, the equivalent diode 15, the regulable amplifier 16 and the adding unit 17. The master-slave current distribution circuit is electrically connected to the parallel power supplies PS1 and PS2, so that the voltage and the current output from the power supplies PS1 and PS2 are stably distributed.
When the power supply PS1 outputs and then the power supply PS2 is connected to the power supply PS1 in parallel by hot plugging, the overshoot surge is formed on the output voltage waveform of the power supply PS1 as shown in FIG. 1(b). However, the regulable output ΔV of the regulable amplifier 16 is added on the output voltage V0 via the current distribution circuit 1, so that the surge is present on the output voltage of the parallel power supplies and the quality of the power supplies are unstable. In order to overcome the disadvantage, there are two methods provided as follows in the prior art.
(1) The maximal value ΔVmax of the regulable output of the regulable amplifier 16 is lowered, so that the surge on the output voltage V0+ΔVmax of the parallel power supplies is lowered. However, if the ΔVmax is lowered to be less than the voltage difference between the power supplies PS1 and PS2, the power supplies PS1 and PS2 can not form the parallel connection, and furthermore the master-slave current distribution circuit can not operate. Therefore, it is limited to lower the ΔVmax of the regulable output by the above method.
(2) A soft-start circuit is added in the master-slave current distribution circuit 1 to lower the surge formed on the parallel power supplies. Please refer to FIG. 1(c) showing the surge of the parallel current distribution circuit lowered by the soft-start circuit. The operation starting point of the soft-start circuit is the point a on the FIG. 1(c), i.e. the operation starting point is not at zero, and the soft-start circuit is operated when the output voltage V0 is output from the parallel power supplies, so that the function of the soft-start circuit is not completely performed and some surge is still formed. The level of the surge depends on the raising time of the output voltage of the power supply PS2, and the level of the surge is higher when the raising time is shorter.
In order to overcome the disadvantages of the prior art described above, the present invention provides a current distribution circuit, which can eliminate the surge formed on the parallel power supplies.